This invention pertains to the art of vehicle control systems and more particularly to a control system capable of generating an air bag deployment signal upon a vehicle collision for an air bag stored in a steering wheel/column and for also transferring a biasing power signal to control circuitry in the wheel for communicating selected driver control signals from the wheel through the column to sensor processing control circuitry. The invention is especially applicable to a control system for transferring signals across a rotating interface. The system is intended to be capable of transferring both an air bag deployment signal and driving control (cruise, climate control, etc.) signals from the steering wheel to the steering column. However, it will be appreciated to those skilled in the art that the invention could be readily adapted for use in other environments as, for example, where a plurality of signals of varying frequency and amplitude need to be communicated through a physically moving part, and in particular a part that is continually rotating.
When vehicle air bags were initially introduced on the market, it was necessary to remove driver control functions from the steering wheel and install them on stalks that emanated from the steering column. Typically, the only two items which remained that were wheel-mounted were the air bag and the horn. The signal for the horn was transferred from the wheel to the column through slip rings. The slip rings consisted of a ball contact located on the steering wheel and a circular conductor which was part of a "clock spring". The clock spring was a molded plastic part which housed a two conductor ribbon cable that connected the air bag to its control module. Such a clock spring is capable of maintaining electrical connections during rotation of the wheel.
As the demand for placement of driver controls back onto the steering wheel has become greater, the clock spring was changed to comprise a housing for a multi-conductor ribbon cable and/or slip ring. This arrangement allowed both the air bag and driver control switches to operate independently on the steering wheel. Some clock springs have as many as six conductor ribbon cables and no slip rings.
The numerous design concepts comprising adaptations of slip rings and clock springs have been fraught with problems and are of limited economic and practical value. Slip ring arrangements have always suffered from reliability and performance problems due to the inherent nature of the slip ring structure itself. The electrical integrity of the contacting methods will necessarily depreciate over time from dirt and/or wear and varying ambient conditions. In addition, the assembly requirements for multi-conductor ribbon cables in a steering column have been notoriously undesirable for the vehicle manufacturers, not only for the relatively high expense of the cable and contact components themselves, but also from the labor costs involved in the assembly operation.
A particular problem with prior known systems which have placed certain driver controls back onto the steering wheel concerns the increased complexity in wheel side electronics. Problems with assembly, maintenance and reliability will always arise as the complexity of circuity increases in an automobile component, such as a steering wheel.
The present invention contemplates a new and improved method and apparatus which overcomes the above-referred to problems to provide a new vehicle steering column control system which is relatively simple in design, economical to manufacture and assemble and provides high reliability and performance in deploying both an air bag ignition signal and communication of biasing power and driver control signals both to and from the steering wheel and the steering column.